The present invention relates to medical stimulators and leads generally, and more particularly to implantable atrial defibrillators.
In the context of an implantable atrial defibrillator, it is generally believed desirable to reduce defibrillation energy thresholds. Because it is anticipated that such devices will likely deliver defibrillation pulses frequently, reduced energy thresholds are perceived as necessary in order to reduce the pain associated with atrial defibrillation pulses to an acceptable level. In the context of proposed prior art atrial defibrillators, a desirable atrial defibrillation threshold is generally stated to be 2 joules or less, preferably 1 joule or less. Numerous patents and applications, attempt to accomplish this goal by optimizing the atrial defibrillation electrode system. Nonetheless, the goal of a defibrillation of an atrial defibrillation lead system which will reliably accomplish such low defibrillation thresholds in all patients remains a difficult one.
One presently pending U.S. patent application Ser. No. 08/293,769, for an Atrial Defibrillator and Method of Use, filed Aug. 19, 1994 by Min et al. discloses an electrode system which appears to generally accomplish a desirably low atrial defibrillation threshold. However, the disclosed electrode system requires multiple atrial defibrillation electrodes to accomplish this result. The simpler right atrium to coronary sinus/great vein pathway, disclosed in U.S. Pat. No. 5,165,403, issued to Mehra provides a desirably low threshold in some patients, but in others requires substantially higher energy levels. The right ventricle to subcutaneous electrode system disclosed in U.S. Pat. No. 5,292,338, issued to Bardy provides the simplest electrode system, allowing use of the same electrodes for atrial and ventricular defibrillation, but requires higher energy levels than desired for atrial defibrillation. The cited Min et al application and the cited Mehra and Bardy patents are incorporated herein by reference in their entireties.